The present invention relates to powder coating spray booths used for containing powder particles that do not adhere to articles intended to be coated. More specifically, the invention relates to a substantially non-conductive spray booth comprising a pair of self-supporting, one-piece, composite, seamless canopy booth halves.
Powder spray booths for electrostatic powder coating operations are well known and are used for environmental purposes to contain oversprayed powder coating material that does not adhere to the target article. In addition, the booth facilitates collection of the oversprayed powder material which is often recycled back into the application system. In an electrostatic powder coating operation, the powder particles are charged, such as by one or more high voltage charging electrodes on an electrostatic powder spray application device, such as a spray gun, and the parts are grounded. The difference in potential creates an attraction of the powder particles to the surface of the parts. Typically, such target parts are overhead conveyed through the booth via one continuous slotted opening extending from one end of the booth through the ceiling and out the opposite end of the booth. The target parts are spray-coated therein as they pass at a controlled rate through the booth.
A powder coating booth and application system must be completely cleaned and purged of one color of powder coating material prior to a successive coating operation using a different powder color. Cleaning a powder coating spray booth can be a labor-intensive effort. In a production powder coating environment, minimizing the system down time to change from one color of powder coating material to another is a critical element in controlling operational costs. Powder material tends to get everywhere within the spray booth during a powder coating operation. During extended powder coating runs, the amount of oversprayed powder accumulated within the booth can impact color change time. Seams between booth panels and recessed ledges, such as where access doors or automatic or manual spray application devices may be located, are typically hard to clean areas and tend to hold concentrations of oversprayed powder coating material that could present a contamination risk after a color change. In addition to seams and ledges and other recesses within the booth, charged powder can adhere to booth interior surfaces.
In typical powder coating booth construction, an outer steel framework is provided for supporting individual panel members which form the roof, side and end walls of the booth. These panel members are known to be made of a thermoformed plastic, such as polypropylene, polyvinyl chloride (PVC), polyvinyl carbonate or polycarbonate. The floor may also be of thermoformed plastic or stainless steel construction. In other known embodiments, powder coating spray booths can have metallic walls, ceilings and vestibule ends, as well a metallic floor and exterior support framework.
U.S. Pat. No. 5,833,751 to Tucker is an example of a powder coating spray booth intended to reduce powder particle adhesion to the interior surfaces of the booth during an electrostatic powder spray operation. Tucker discloses a booth chamber comprising a pair of thermoformed plastic shells with smooth curvilinear interior surfaces that are intended to inhibit oversprayed powder particle adhesion. Two identical ends connect with the shells and an external support frame is disclosed, but not shown. Possible booth materials disclosed include polyvinyl carbonate and polycarbonate.
Known booth materials are available in limited sizes requiring some method of seaming to generate the overall size. These seams require much effort and cost to achieve a virtually uninterrupted, seamless surface.
In addition, known powder coating spray booths have numerous features that reduce operational efficiencies. These suboptimal features are evidenced during powder coating color changes between successive runs of different coating colors and during assembly and maintenance of the booth itself. Known powder coating spray booths use metallic external support frames and stainless steel or thermoplastic, floors, walls and ceilings. During an electrostatic powder spray coating operation, oversprayed powder material can actually be attracted and adhere to these booth interior surfaces. Higher concentrations of oversprayed powder coating material are typically seen in the immediate vicinity of the highly conductive steel frame members, which are typically grounded or are somewhat insulated from ground and could act as capacitors. Although thermoformed plastics are typically thought of as insulators, their insulative properties vary and powder particle adhesion can vary with the conductivity and resistivity of these materials. With age, conductivity of the thermoformed plastic materials can increase with corresponding increases in powder particle adhesion, as they can absorb moisture from the ambient air over time. Ultraviolet light is also known to change the physical properties of thermoplastics over time.
In addition, typical booths have numerous design features that act to increase accumulated oversprayed powder coating materials in the spray booth, thus increasing cleaning times during color change operations. In booths using panel members connected with each other and supported by an external frame, numerous seams exist throughout the booth interior that entrap oversprayed powder coating material, thereby making the booth harder to clean during a color change or routine booth maintenance. In addition to the seams, ledges are present in some powder coating spray booths on which spray gun application devices rest and are mounted, and where openings for doors and other access portals are reinforced and secured, for example. These ledges can either extend into the booth or, more typically, extend away from the inner surface of the booth. Even if otherwise angled or curved toward the floor from the typically vertical sidewalls, oversprayed powder coating material still tends to accumulate in these areas, thus making them more difficult to clean, as well.
In addition to the reduced spray booth operating efficiencies due to powder coating material adhesion as a result of electrostatics and booth design, booths constructed with frames and panel members and booths made of thermoformed plastics increase assembly and maintenance times, thus further reducing operational efficiencies. Known booths require external frames for structural support. Booths constructed of numerous individual wall and ceiling panel members must have their seams welded or otherwise sealed together. Installation of booths that require external frames for structural support of any kind increase booth installation time. Booths having multiple panels forming the walls, ceiling and floors further increase assembly time, and at best result in a semi-rigid enclosure that falls short of a preferred robust containment envelope that is suitable for industrial environments.
Maintenance of thermoformed plastic booths is also a concern and has a negative impact on efficient booth operations. With thermoformed plastic booth materials, workers and parts can accidentally nick and scratch the booth internal surfaces rather easily. These surface imperfections and discontinuities are hard to clean areas and act to entrap powder coating material therein. In addition to increased cleaning times, maintenance of the booth to remove the scratches and nicks are time-intensive at best, and results of repair activities cannot restore a surface to original condition. Both the ease at which thermoformed plastic booths can be scratched and the time involved in repairing them make thermoformed plastic booths less than ideal as a powder coating booth material.
It is desired, therefore, to provide a powder coating booth that overcomes these and other shortcomings.
The invention herein provides for an improved powder coating spray booth. In one embodiment, which is well-suited for retrofitting existing powder coating spray booths, the invention herein comprises a pair of opposed canopy halves that each have a sidewall and a ceiling portion that can be connected to each other through a radius. This radius serves to reduce color change times and functions as a torsional support element for the wall and ceiling surfaces. Each canopy half is a seamless, composite, unitary structure that can connect with an existing booth floor and with the existing booth vestibule and/or aperture end or ends, and can be separated at the top providing for a narrow overhead conveyor slot opening typical in electrostatic powder coating spray booths. The canopy halves are each self-supporting, which means they can be assembled together with an existing floor and vestibule end or ends and no external frame is required to support the powder coating spray booth of the present invention. By removing the external frame typical of all known powder coating spray booths and constructing the inventive booth canopies from nonconductive materials, the improved booth can be assembled much quicker and is more nonconductive to oversprayed electrostatic powder particles. Thus, less oversprayed particle coating material adheres to the ceiling and walls of the inventive booth. Of course, it can be appreciated by those skilled in the art that this improved embodiment of the invention can also work equally well with a new floor or vestibule end.
The canopy halves of the present invention are made from a number of non-conductive materials that are loaded onto a set-up tool having a smooth surface that has been prepared with a release agent. All the materials can be non-metallic. Typical non-conductive layers can include a first, optional, sprayed on layer of gel-coat, which is an unreinforced resin layer that is allowed to set or cure. This first layer of the booth canopy halves serves as the booth interior surface. It may be pigmented, such as with white pigment, for aesthetics and functional reasons, such as to give a clean smooth appearance and to help the worker identify the location of oversprayed powder coating material within the spray booth during booth cleaning for a color change. The specific resin material chosen is non-conductive, ultraviolet light stable and impervious to moisture adsorption, even over time. This layer can be followed by an optional layer of chopped strand mat which is a random orientation glass fiber product. Also included are three necessary layers including a core having a suitable thickness to give the canopy halves structural rigidity and a first and a second layer of knitted glass fabric sandwiching the core for strength. One or more handling tabs can be placed within the lay-up of the composite canopy halves, such as at perimeter edges or at the outer radius between the ceiling and wall portions, to assist with handling the composite canopy halves during lifting the newly formed canopy half from the tool, secondary operations in finishing the canopy half, storage, transportation and booth assembly at a production site. These handling tabs can be simple nonconductive lugs, such as of similar composite construction and already cured before placement in the lay-up.
These layers are infused with a non-conductive resin and allowed to cure, thereby forming a composite structure that is strong, lightweight, nonconductive and can be repeatably reproduced on the same tool. The infusion and curing of the resin in the layered composite booth halves are done under a bag that is sealed to the set-up tool and evacuated at room temperature in a process that removes all voids and gives repeatable results. One such process is known as Seeman Composites Resin Infusion Molding Process (xe2x80x9cSCRIMPxe2x80x9d). SCRIMP and improvements thereto are covered in U.S. Pat. Nos. 4,902,215, 5,052,906 and 5,439,635, all to Seeman, hereby incorporated by reference in their entirety herein.
The cured canopy halves can be lifted off the set-up tool, trimmed and have their access and other operational openings cut. A final exterior layer of gelcoat, again a pigmented or unpigmented unreinforced resin layer can be applied for aesthetics and to further inhibit moisture adsorption over time and during shipping to the production site. Alternatively, an epoxy-based barrier coat can be applied in place of the gelcoat for the same purposes. Either coating layer on the part exterior serves to effectively seal the part from the elements during shipping and fills in any pinholes that may be present on the exterior or trimmed surfaces of the composite canopy half.
In accordance with another aspect of the invention, each canopy half of the inventive spray booth can be essentially mirror images of each other and produced with the same tooling. As such, they can be shipped to the production site in a nested configuration, minimizing shipping space. In addition, each canopy half can have one or more access and other operational openings which are positioned in the canopy half during construction by measured placement of the core material, essentially removing the core material where an access opening is desired. A flange around the perimeters of the canopy halves can be provided by tapering the core layer to zero thickness and creating a flange from the remaining layers, as described above. These perimeter flanges can be used for connecting the floor and the booth ends, which can be narrowed vestibules that are known to help retain oversprayed powder coating material inside the spray booth. Alternatively, one or both of the vestibule ends can be replaced with aperture bulkheads that establish a part opening in the booth end or ends.
Access openings can similarly have such perimeter flanges, to which can be exteriorly or interiorly connected doors, application device supports, cyclone powder recovery units, and the like. Alternatively, man-door access openings and other operational openings, such as for automatic gun slots and manual gun openings, can also be located throughout the booth walls and not require the pre-established, measured core windows where the core material has been purposefully removed. The man-door access and other operational openings can be created through cut outs of the full-thickness composite, including the core material layer, with the resulting edges treated with a barrier coat during secondary operations, as described supra.
In another embodiment of the invention, each composite, seamless, unitary canopy half of the inventive booth comprises a ceiling portion, a sidewall and, additionally, a floor portion. The sidewall can connect to the ceiling and to the floor through respective radii. These canopy halves are similarly constructed as described above on a suitable tool surface and may also have one or more access openings and handling tabs. In addition, the floors of the respective canopy halves can each have a downwardly extending flange for connecting with the respective canopy half floor flange. Alternatively, the respective floor portions can be connected via a bonded shiplap type of joint or a bonded spline joint using a continuous glass fiber spline, for example. It will be appreciated by those of skill in the art that other joining methods may be used without departing from the scope of the present invention. In this inventive booth embodiment, a utility base can be included wherein the mated booth canopy halves can sit atop and may be connected thereto. Again, an existing or a new vestibule and/or aperture bulkhead end or ends can connect to the perimeter flanges of the sidewall edges of the present embodiment. In this embodiment, only one centerline floor seam exists, versus the aforementioned embodiment which connects to a separate floor, thus having two sidewall-to-floor seams that must be sealed and prior to use.
In another embodiment of the invention, a method is disclosed for assembling a powder coating spray booth. The method includes providing a pair of canopy halves that are each a seamless, nonconductive, self-supporting structure having a ceiling and a sidewall, and connecting a perimeter edge of their respective sidewalls to a floor. The canopy halves can be non-metallic. Their composite construction consists of the nonconductive layers as described in the canopy halves described above. A vestibule or aperture bulkhead end can be connected to either or both perimeter flanges of the sidewall edges of the each of the canopy halves. Assembly of such an inventive booth is less labor intensive than any known booth. No external frame is required to support the assembled booth.
In another embodiment, another method is provided for assembling a non-conductive powder coating spray booth. In this embodiment, the pair of canopy halves of the inventive method each comprise a ceiling, sidewall and floor portions. A utility base is provided and placed where desired. The respective canopy booth halves are connected to each other at a respective floor edge flange, or other joint, and placed atop the utility base. The canopy halves can be connected to the utility base. The canopy halves can have respective perimeter edge flanges along each of the common floor, sidewall, and ceiling edges and be connected to a vestibule or aperture bulkhead end or ends at either or both of the respective perimeter edge flanges. The canopy halves can be substantially nonconductive. The utility base can be made of carbon steel.
In another inventive powder coating booth embodiment, a nonconductive, self-supporting, spray booth canopy is provided that includes a pair of composite canopy halves each having a wall and ceiling portion and at least one integral vestibule end half, or aperture bulkhead half. In addition, each canopy half can have an integral floor portion with the assembled canopy halves requiring a suitable utility base section for connecting thereto. The integral floor portions of either half, or both halves may be sloped to facilitate oversprayed powder coating material collection in one or more collection troughs located below the booth floor. Otherwise, a floor is provided to connect with the canopy halves at perimeter wall and vestibule or aperture bulked edges. An overhead conveyor slot opening for passing parts through the booth can be provided. The canopy halves are nonconductive for minimizing the adherence of electrostatically charged oversprayed powder coating material to the booth interior surfaces.
Various other embodiments of the invention are described and claimed herein, and other features and advantages of the present device will become apparent from the following detailed description, with reference to the accompanying drawings and claims, which form a part of the specification.